1. Field of the Invention
The present invention is primarily directed to a mobile sewer cleaning apparatus having a rotating drum and a flexible hose wound thereon. Preferably mounted on the sewer cleaning apparatus is a device for measuring the length of hose paid out from the drum. The measuring device may be used, among other things, for measuring the speed of the hose as it is wound or unwound from the drum, and for controlling a safety device intended to stop the flow of water through the hose as the hose is being wound.
2. Background Information
Numerous devices which make it possible to measure the length of a substantially continuous object, or to measure the positioning of an article in an environment, are known. Such devices have been disclosed in relation to apparatus for the cleaning of a sewer or drain. For example, the use of optical means for the detection of the positioning of an object is disclosed in U.S. Pat. No. 4,700,422 (RUSSELL) and French Patent No. 2,609,417 (VAIRE). The latter French patent discloses the use of a video camera for marking the positioning of a sewer flushing device, which camera may also be stabilized by lateral jets.
Generally, such devices as mentioned above have also been disclosed for applications in the field of textiles, for applications with very long articles, and for applications with individual objects in the field of anti-theft protection. Such devices generally make use of detection either by mechanical means, by optical means, or by electrical or electronic means.
Generally, the most common mechanical device for the measurement of length make use of the counting of the number of revolutions of a drum or support of the very long, flexible article being measured. Such devices are used particularly in the textile industry. For example, such devices are used for the measurement of the length of wool threads of a loom, as disclosed in Belgian Patent No. 889 255 (WEEFAUTOM PICANOL), U.S. Pat. No. 3,915,199 (TEIJIN), and Japanese Patent No. 61 174 447 (TOYODA AUTOMAT LOOM).
Various electrical, electronic and even magnetic or electromagnetic means have been proposed. For example, USSR Inventor's Certificate No. 1,121,581 (PETROV) discloses means for the determination of the length of an elastic fabric. French Patent No. 2,389,139 (SOCOTEC) discloses means for the detection of a defect in cables embedded in concrete. U.S. Pat. No. 3,990,065 (MAGNAVOX) and French Patent No. 2,379,871 (KNOGO) both disclose means for the detection of thefts of objects in warehouses. Most particularly, means for the identification of articles by reading a recently developed "bar code" is the subject of numerous patents, including French Patent Nos. 2,616,565 (LACROUTS-CAZENAVE) and 2,615,983 (SOGEDEC).
Generally, all of the devices of the known art relating to the determination of the length, speed or positioning of an object have various disadvantages. Among these disadvantages are: for mechanical devices, a lack of precision; for electromagnetic detection systems, the complexity of the detection installation, which installation tends only to be designated for the application at hand; the difficulty of using optical devices in locations which are not well lit, including the need to utilize a supplemental light source, which is not always easy to manage; and, in a great many applications, such as applications for the reading of "bar codes" or for anti-theft devices, the necessity for providing visible markings, of which the aesthetics are debatable, and which tend to limit the usefulness of the article or must be removable after detection, such as for the magnetic markings applied to articles of clothing.
Additionally, the invention may relate more generally to the linear measurement and positioning of very long, flexible articles. The invention makes use of concealed markings which can be detected by means of an associated reader device preferably incorporating electromagnetic means. In other applications, the invention may be used for the measurement of the speed of movement, or for the marking of lengths, of a very long, flexible article. Furthermore, the invention may be used for the detection of the position of a given portion, such as an extremity, of a very long, flexible article.